Lecture 20 - Disease Production - Transmission
Introduction to Disease Production Transmission Organism has to get to you from another host in order to cause disease. Portal of Entry Pathogen must enter through the right way to cause disease. Period of Incubation The organism needs time to grow, or increase in load (number). Little to no symptoms shown during this period. Demonstration of Virulence The method through which the organism causes harm. Invasiveness Production of toxin Signs and symptoms Host's reactions to the pathogen. Portals of Exit Method by which the organism leaves one host to transmit to another host. Transmission There are different ways to transfer a pathogen from one host to another. They are categorized as following: vector and vehicle, and active and passive. Vectors are alive, and vehicles are non-living. Passive vectors or vehicles, also referred to as mechanical or source, carry the pathogen but the pathogen is not increasing in number. Active vectors or vehicles, aka reservoirs of infection, provide a means of transmission for the disease, and promotes the growth and survival of the pathogen. Active vehicles can include soil (for anthrax), rust (for tetanus), and water. The six main modes of transmission that will be covered are: # Fingers # Flies # Fomites # Food # Phlegm # Fun ID 50 The infectious dose 50 is the amount of bacteria required to infect half the population that you expose the dose to. The 50% infected will usually have a lower immune system due to alcoholism, poor nutrition, or advanced age. Control of Transmission of Infectious Diseases Eliminate Reservoirs Small pox Wiped out reservoirs of small pox with vaccines. CDC keeps samples of the virus for research. Trying to do the same for polio, but anti-vaccine movements happened. Malaria Humans tried to eliminate mosquitoes, unsuccessfully. In the past, insecticides such as DDT killed many birds and other things than insects. Black Plague/Death Caused by Yersinia pestis carried by fleas on rats, prairie dogs, and mice. In the past they tried to eliminate rats, but only managed to reduce their numbers. Break the link in transmission Cow milk can contain Mycobacterium bovis, but pasteurization breaks the link in the transmission of the pathogen. Human feces can spread E. coli, Salmonella, and Cholera, but the water is chlorinated to disinfect it before it can be transmitted to the human again. Condoms can prevent the spread of STDs such as AIDS, ebola, gonorrhea. Immunizing Biologics (vaccines) If the other methods of controlling the transmission don't work, there are always vaccines. You know what vaccines do. Pertussis - carriers can cough a lot and spread to everyone. Adults will only show mild symptoms and spread it to children, who are much more susceptible to pertussis and will likely die (if not vaccinated) Tetanus - Clostridium tetani can form spores, which makes them highly resistant to the other methods of control. They are transmitted by cuts, and are very common. Diphtheria - Many people are considered carriers but aren't really affected by it. Diphtheria is still dangerous when passed on to an infant.